Have a look at this:

http://www.microsoft.com/security/en...32/Mywife.E@mm

On the third day of every month the worm resets the content of files with specific extension. It searches for files on the hard disk with the following extensions and replaces their contents with "DATA Error [47 0F 94 93 F4 K5]":
The last bit of the article gives suggestions for recovery.

Good luck